After a cat eats a foreign body, it needs to be fed some probiotics to promote gastrointestinal motility. You can also feed cat grass or hair removal cream to promote vomiting. These two methods can expel or vomit the foreign body, which usually takes two days. The foreign body can be expelled in about three days. If the foreign body is not expelled for more than three days, it is best to send the cat to the pet hospital for treatment immediately, otherwise it may easily cause intestinal obstruction in the cat.